Generally, an experienced operator of a reversing rolling mill will adjust his mill settings according to his prior experience with the same mill on a previous occasion. It will be readily appreciated, however, that such a method is almost totally dependent upon the skill of the operator and is replete with inefficiencies.
There are several reasons why the method of managing the operation of the rolling mill is inefficient. First, the operator may not have previously rolled the same material, or, if he has, he may not have worked with the same starting and finishing gauges. Alternatively, he may not have experience with the particular material being rolled on the rolling mill in question. In such cases, he cannot rely upon his experience and is relegated to trial and error estimates on every pass. It is then almost impossible to roll efficiently. When the operator is not very experienced, the problem is accentuated further.
Moreover, if the rolling mill is operated on a shift basis, as is normal, then each mill operator will set up the mill differently, according to his own previous experience. As a consequence, there are normally large variations in rate of production and product quality achieved from shift to shift.
Further, if a plant has several different rolling mills, and there is a need to transfer an operator from one mill to another, the operator's previous experience is of limited value. If the second mill (including its drive) is not identical in all respects to the first, the permissible pass reductions may be greater or less than those for the first mill.
Even when a skilled operator has machine specific experience, it is common for inefficiencies to arise. When the strip thickness is approaching the finished gauge, for example, an operator frequently has great difficulty in determining intermediate gauges. He might, for example, have to decide at a certain point whether to make another 2 or another 3 passes. Even if he chooses the most efficient number of passes, he then has to guess at the appropriate intermediate gauge(s).
One prior art method of rolling mill management, which, to some extent overcomes some of the problems outlined above, is the so-called "programmed pass schedule" method. With this method a rolling schedule for a given material, width, starting and finishing gauges, (and a given rolling mill) is stored in a computer memory. When it is desired to repeat that schedule with a fresh coil, the mill settings for each pass are recalled from the memory and the operator sets the mill (or the mill is set automatically) to these settings.
This programmed pass schedule method may be satisfactory when the range of materials, starting and finish gauges, and widths is very small. However, if the range is large, the amount of memory needed, and the amount of labor needed to determine all possible schedules and store them in the memory become prohibitive.
Even when the range of materials, gauges, etc. is small, the following problems still remain:
(1) Any particular schedule stored may not utilize the mill load capacity and mill drive capacity fully.
(2) The schedule will, in general, be only good for the one mill.
(3) The schedule does not allow for variations in work roll size (as these rolls wear), nor does it allow for the fact that mills can frequently operate at higher power levels (and thus be more productive) in winter than in summer.
(4) The schedule cannot allow for operator intervention. Since the operator may have to change an intermediate gauge for a number of reasons, he would then be obliged to reschedule all remaining passes, since the programmed pass schedule will no longer apply.
(5) There will still be some coils to be rolled having combinations of material type, width and gauges which will not be stored in the memory. For any such coils, the operator must determine mill settings by trial and error.